Calenderable thermoplastic polymer compositions

ABSTRACT

A thermoplastic polymer composition comprising 
     (a) 50-90 wt. % of a polymer blend comprising 
     (i) 10-40 wt. % polypropylene 
     (ii) 15-50 wt. % uncrosslinked ethylene propylene copolymer rubber having an ethylene content of 60-80 wt %, 
     (iii) 20-60 wt. % of an ionomeric copolymer of ethylene and an α,β-unsaturated C 3 -C 8  carboxylic acid, and 
     (iv) 0.1-5 wt. % of a copolymer of ethylene and glycidyl acrylate or glycidyl methacrylate, 
     (b) 10-40 wt. % inorganic filler and 
     (c) 0-15 wt. % of an uncrosslinked ethylene propylene copolymer rubber having an ethylene content of 60-80 wt. % grafted with 0.01-5 wt. % of an α,β-unsaturated carboxylic acid or an anhydride thereof.

BACKGROUND OF THE INVENTION

This invention relates to thermoplastic polymer compositions which arethermoformable, and to thermoformed articles made from suchcompositions.

The compositions of the present invention, which are halogen-free, areuseful for making laminates, sheets and films, and for replacingpolyvinyl chloride (PVC) resins in many of their tradition uses. Inparticular, compositions of the present invention, and thermoformedarticles made therefrom, are suitable as PVC replacements in theautomotive field. They may be used in the fabrication of interiorsheating of automobiles, for example, in the instrument panel skins,door panels, roof liners and seat covers.

Automotive applications require certain properties in the resins,including good flexibility, low temperature properties, capability ofproviding a soft surface texture and grain retention: as well as goodhigh temperature properties and low emissions associated with it in viewof the extreme temperatures the interior of automobiles can reach onhot, sunny days.

Non-halogenated thermoplastic compositions having good high temperatureproperties are known in the art, for example the polyolefin/ionomerblends disclosed in U.S. Pat. No. 4,871,810, or the blends of partiallycrosslinked ethylene/α-olefin copolymers with reaction products ofethylene copolymer ionomers and olefin/epoxy copolymers, disclosed inU.S. Pat. No. 4,968,752. Such compositions, however, are deficient insoftness.

The deficiencies of the prior art compositions have been largelyovercome by a composition comprising a blend of polypropylene, ethylenecopolymer ionomer resin, ethylene/glycidyl acrylate or methacrylatecopolymer, and uncrosslinked ethylene propylene rubber as described inU.S. Pat. No. 5,206,294. Such a blend has been proven suitable for mostapplications and it is characterized by good thermoformability and grainretention. These blends, however, are not calenderable. The presence ofionomer resin and ethylene/glycidyl acrylate or methacrylate copolymerleads to excessive sticking of the blend on metal rolls of theprocessing equipment. As certain processors are equipped only withcalendering equipment. As certain processors are equipped only withcalendering equipment (not with extrusion equipment) there is acommercial need for thermoplastic polymer blends suitable for makingthermoformed articles by calendering, which articles demonstrate therequisite flexibility, temperature properties, capability of providing asoft surface texture and grain retention for automotive applications.

SUMMARY OF THE INVENTION

In accordance with the present invention, thermoplastic polymercompositions are provided comprising

50-90 wt. % of a polymer blend comprising

(i) 10-40 wt. % polypropylene

(ii) 15-50 wt. % uncrosslinked ethylene propylene copolymer rubberhaving an ethylene content of 60-80 wt. %,

(iii) 20-60 wt. % of an ionomeric copolymer of ethylene and anα,β-unsaturated C₃-C₈ carboxylic acid, and

(iv) 0.1-5 wt. % of a copolymer of ethylene and glycidyl acrylate orglycidyl methacrylate,

(b) 10-40 wt. % inorganic filler and

(c) 0-15 wt. % of an uncrosslinked ethylene propylene copolymer rubberhaving an ethylene content of 60-80 wt. % grafted with 0.01-5 wt. % ofan α, β-unsaturated carboxylic acid or an anhydride thereof.

These compositions exhibit excellent flexibility, temperatureproperties, capability of providing a soft surface texture and goodgrain retention. The present invention is also directed to thermoformedarticles from such compositions, particularly instrument panel skins.

DETAILED DESCRIPTION OF THE INVENTION

The polymer blend component (component (a)) of the thermoplastic polymercomposition of the present invention is present in amounts of 50-90 wt.%, preferably 55-85 wt. %.

The polypropylene component of the polymer blend (component (a)(i)consists of crystalline polypropylene and is intended to include inaddition to the homopolymer those polymers that also contain minoramounts, usually not greater than 15 weight percent, of higher or lowerα-olefins, e.g. those containing 3-8 carbon atoms, such as ethylene,butene, octene, etc. The polypropylene polymers useful in this inventionhave melt indices in the range of from about 0.07-30 dg/minute at 230°C./2.16 g, and are present in the blend in amounts of 10-40 wt. %,preferably 15 to 30 wt. %.

The uncrosslinked ethylene/propylene copolymer rubber (component (a)(ii)and which serves as the base of component (c)) may be anethylene/propylene/nonconjugated diene copolymer (EPDM) or anethylene/propylene copolymer (EPM). EPDMs are preferred as component(a)(ii); EPMs are preferred as the base of component (c). Theuncrosslinked ethylene/propylene copolymer rubber contains about 60-80wt. %, usually about 65-75 wt. % ethylene.

The nonconjugated dienes can contain from 6-22 carbon atoms having atleast one readily polymerizable double bond. The amount of nonconjugateddiene is generally from about 1-7 wt. %, usually 2-5 wt. %. EPDMcopolymers that are especially preferred areethylene/propylene/1.4-hexadiene, ethylene/propylene/dicyclopentadiene,ethylene/propylene/norbornene, ethylene/propylene/methylene-2-norborneneand ethylene/propylene/1,4-hexadiene/norbornadiene. It is preferred thatthe ethylene/propylene copolymer rubber are non-crosslinked. Theethylene/propylene copolymer rubber present as component (a)(ii) in theblend is present in amounts of 15-50 wt. %, preferably 15-40 wt. %.

The ionic copolymer of ethylene and an α,β-unsaturated C₃-C₈ carboxylicacid (component (a)(ii) optionally contains at least one softeningcomonomer that is copolymerizable with ethylene. Acrylic and methacrylicacids are preferred acid comonomers. The softening comonomer can be analkyl acrylate selected from the group consisting of n-propyl-, n-butyl,n-octyl, 2-ethylhexyl-, and 2-methoxyethyl-acrylates. The preferredalkyl acrylates are n-butyl-, 2-ethylhexyl-, and2-methoxyethyl-acrylates. The softening comonomer can also be an alkylvinyl ether selected from the group consisting of n-butyl, n-hexyl,2-ethylhexyl-, and 2-methoxyethyl-vinyl ether. The preferred alkyl vinylethers are n-butyl vinyl ether and n-hexyl vinyl ether. The coplymer isabout 10 to 70% neutralized with metal ions selected from groups Ia, Ib,IIa, IIIa, IVa, VIb, and VIII of the Periodic Table of Elements such assodium, potassium zinc, calcium, magnesium, lithium, aluminum, nickel,and chrominum. Preferably the copolymer has from about 35 to about 70%of the carboxylic acid groups ionized by neutralization with metal ionsselected from the group consisting of sodium, potassium, zinc, calcium,and magnesium. The ionomeric copolymer is present in the blend inamounts of 20-60 wt. %, preferably 30-50 wt. %.

The copolymer of ethylene and glycidyl acrylate or ethylene and glycidylmethacrylate (component (a)(iv)) preferably contains copolymerized unitsof an alkyl acrylate or an alkyl methacrylate having 1-6 carbon atoms.The ethylene/glycidyl acrylate or ethylene/-glycidyl methacrylatecopolymer contains 60-88 weight percent ethylene and 1-12 weight percentglycidyl acrylate or glycidyl methacrylate. Representative alkylacrylates and alkyl methacrylates that are used in the copolymer includemethyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate,isobutyl acrylate, hexyl acrylate, methyl methacrylate, ethylmethacrylate, propyl methacrylate, butyl methacrylate, and hexylmethacrylate. Ethyl acrylate is preferred and n-butyl acrylate isespecially preferred.

The ethylene/glycidyl (meth)acrylate copolymer can be prepared by directpolymerization, for example, copolymerizing ethylene, an alkyl acrylate,and glycidyl methacrylate or glycidyl acrylate in the presence of afree-radical polymerization initiator at elevated temperatures,generally 100°-230° C., and at elevated pressures, i.e. 140-350 MPa. Themost preferred ethylene/glycidyl(methacrylate copolymers that are usedin this invention are copolymers of ethylene, ethyl acrylate, glycidylmethacrylate, and, especially, ethylene, n-butyl acrylate, and glycidylmethacrylate. The copolymer of ethylene and glycidyl acrylate orethylene and glycidyl methacrylate is present in the blend in amounts of0.1-5 weight %, preferably 2-5 weight %.

A wide range of particulate inorganic fillers (component (b)) may beused depending on the intended use of the composition and, if desired, amixture of particulate inorganic fillers may be used. The particulateinorganic fillers is suitably a basic filler for example an oxide, ahydrated oxide, a hydroxide, a carbonate or a mixture thereof, andespecially is predominantly on oxide, a hydrated oxide, a hydroxide orcarbonate of a metal of group II or III, such as magnesium, calcium oraluminium or a mixture thereof. The particulate inorganic filler istypically a material of the type which is used as an intumescent fillerfor a plastic material. The inorganic filler may a hydroxycarbonate suchas hydrated magnesium hydroxy carbonate which occurs naturally ashydromagnesite, a mixed carbonate such as magnesium-calcium carbonate ormay be a mixture of two or more such materials. Preferred inorganicfillers are calcium carbonate, talc, mica and gypsum, more preferablycalcium carbonate or talc. The inorganic filler will be present in thepolymer blend in an amount of 10-40 wt. %. In cases where there is nocomponent (c) present, there is preferably 20-40 wt. % inorganic fillerpresent. In cases where component (c) is present, there is preferably10-30% inorganic filler present.

The grafting monomer suitable for grafting the uncrosslinked ethylenepropylene copolymer rubber (the resulting grafted rubber being component(c)) is at least one of α, β-ethylenically unsaturated carboxylic acidsand anhydrides thereof, including derivatives of such acids andanhydrides, which may be mono-, di- or polycarboxylic acids, are acrylicacid, methacrylic acid, maleic acid, fumaric acid, itaconic acid,crotonic acid, itoconic anhyddride, maleic anhydride and substitutedmaleic anhydride e.g. dimethyl maleic anhydride. Examples of derivatesof the unsaturated acids are salts, amides, imides and esters e.g. mono-and disodium maleate, acrylamide, maleimide and diethyl fumarate. Maleicanhydride is preferred. The amount of grafting will be 0.01-5 wt. %,preferably 0.1-3 wt. %, based upon the weight of the uncrosslinkedethylene propylene copolymer rubber in component (c). Grafting processesare known in the art. The melt viscosity of the grafted uncrosslinkedethylene propylene copolymer rubber is not restricted, however, mostpreferred is found if the meld index, measured at 2.16 kg and 190° isbetween 50 and 150 g/10 min. or if the melt flow index, measured at 2.16kg and 280° C. is 5-30 g/ 10 min. The grafted uncrosslinkedethylene/propylene copolymer rubber will be present in the polymercomposition in an amount of 0-15 wt. %, preferably 1 to 10 wt. %.

The thermoplastic polymer compositions of the present invention aregenerally prepared by melt blending the polymeric components under highshear conditions, for example in an extruder. The various ingredientsmay first be combined with one another e.g., in a pellet blend, or theymay be combined with one another via simultaneous or separate meteringof the various components. They may also be divided and blended in on ormore passes into separate sections of the mixing equipment.

The resultant compositions may be thermoformed into a variety ofarticles, including sheets, or they may be molded into any desiredshape. In particular, they may be thermoformed at high deep-draw ratiosfor use as instrument panel skins for automobiles. Excellent lowtemperature flexibility and high temperature resistance enables thesecompositions to be useful in applications wherein a wide range oftemperature and abrasive conditions are encountered. In addition, asthese compositions resist sticking to metal at elevated temperatures,e.g. 150-200° C., they can be used in processes in which hot polymercomes into pressure contact with hot metal rolls.

The invention can be further understood by the following examples inwhich parts and percentages are by weight unless otherwise indicated.

EXAMPLES

Sheets of thermoplastic polymer compositions are formed by blending a“salt and pepper” mixture of granules of polymers and fillers on alaboratory two mill for 3 min. at 170-190° C. The releasability of thesheets from the calender rolls of the mill are judged subjectively:

1=very good release—can be drawn off by hand

2=good release—similar to 1 by higher force required

3=poor release—doctor knife required for removal

4=very poor release—sticks entirely to the rolls and cannot be releasedat all as a continuous sheet

Milled sheets removed from the rolls are pressed in a hydraulic press at220° C. in order to prepare a 12 mm×12 mm×2 mm plaque on which tensilestrength, elongation, secant modulus and hardness are determinedaccording to DIN 57504

In addition, compositions are compounded in a 25 mm PRISM twin screwextruder. All ingredients are prepared as a “salt and pepper” blend andgranulated after exiting the extruder. The granulate so obtained ismelted on a two roll mill and blended at 190° C. to give a feedstock fora lab calender which is run at 180° C.

All compositions are based on the following thermoplastic polyolefin(TPO) composition (amounts given in wt. %)

Polypropylene¹ 20 EPDM² 44 Zn Ionomer³ 32 ENBAGMA⁴ 2 Carbon black 2¹melt index 4 g/10 min., ASTM D-1238, Condition L ²70 wt. % ethylene/26wt. % propylene/4 wt. % 1,4-hexadiene ³29.5 wt. % ethylene/22 wt. %n-butyl acrylate/8.5 wt. % methacrylic acid, 45% neutralized with zinc⁴66.7 wt. % ethylene/28 wt. % n-butyl acrylate/5.3 wt. % glycidylmethacrylate

To this formulation is added the following processing aids, iorganicfillers and other additives.

Ingredient Obtained from Zinc stearate Merck, Germany MICROLINE A3 talcNaintsch, Austria EXTRA PUR CaCO₃ Merck, Germany Fusabond MF416D⁵ DuPontFusabond MD353D⁶ DuPont MB50-002⁷ Dow-Corning ⁵EPM grafted with maleicanhydride ⁶polypropylene grafted with maleic anhydride ⁷A masterbatch of50 wt % silicone in polyethylene

Compositions in wt % (‘C’=comparative example; ‘E’=inventive example)

C1 C2 C3 E1 E2 E3 E4 TPO 100 95 98 90 80 70 90 MB50-002 5 Zn Stearate 2Talc A3 10 20 30 CaCO₃ 10 Rating 4 4 4 3 3 2 3 E5 E6 E7 C4 E8 E9 E10 TPO70 75 75 65 75 70 56 Zinc stearate Talc A3 10 10 20 15 15 25 15 CaCO₃ 1515 15 22 Fusabond MF416D 5 5 10 5 7 Fusabond MD353D 5 Rating 1 2 2 4 3 31

We have found that common processing aids such as silicons, andfluoropolymer processing aids such as PTFE micro-powder sold as ZONYL MP1500 (available from DuPont) do not enhance calenderability in theseformulations, although they have been proven to be effective in reducingsticking to metal and many other substances.

As is indicated by the test results, the inorganic fillers with theionomer and ENBAGMA to reduce the adhesion to the metal rolls of thecalender and the roll mill. Comparative Example C4 shows that graftedpolypropylene does not lead to any improvement in terms of sticking tometal, and in fact, reverses the positive effect of the filler.

What is claimed is:
 1. A thermoplastic polymer composition comprising(a) 50-90 wt. % of a polymer blend comprising (i) 10-40 wt. %polypropylene, (ii) 15-50 wt. % uncrosslinked ethylene propylenecopolymer rubber having an ethylene content of 60-80 wt. %, (iii) 20-60wt. % of an ionomeric copolymer of ethylene and an α, β-unsaturatedC₃-C₈ carboxylic acid, and (iv) 0.1-5 wt. % of a copolymer of ethyleneand glycidyl acrylate or glycidyl methacrylate. (b) 10-40 wt. %inorganic filler, and (c) 2-15 wt. % of an uncrosslinked ethylenepropylene copolymer rubber having an ethylene content of 60-80 wt. %grafted with 0.01-5 wt. % of an α,β-unsaturated carboxylic acid or ananhydride thereof.
 2. A thermoplastic polymer composition according toclaim 1 wherein component (b) is selected from calcium carbonate, talc,mica and gypsum.
 3. A thermoplastic polymer composition according toclaim 1 wherein component (c) comprises 2 to 10 wt. % of the compositionand is an ethylene/propylene/nonconjugated diene copolymer grafted with0.1-3 wt. % maleic anhydride and has a melt flow index at 280° C/2.16 kgof 5-30 g/10 min.
 4. A thermoplastic polymer composition according toclaim 3 wherein component (b) comprises 10-30 wt. % calcium carbonate ortalc.
 5. A thermoformed article made from a composition according to anyone of claims 1 to
 4. 6. A thermoformed article according to claim 5wherein the article is an instrument panel skin.